Wiki info about Me 163 B

The Messerschmitt Ме 163 Komet was a German rocket-powered interceptor. Its first flight took place on 1st September 1941. A very small number was produced; only 91 before the end of 1944. First combat for the Komet took place on 14th May 1944.
The Me 163 was a unique aircraft standing virtually alone in aviation history. The Komet was the only operational tailless aircraft and the only operational rocket fighter of WWII. In addition, it had other unique features, including its very narrow role, a daylight short-range interceptor used for pin-point defense of strategic targets, with a record-breaking top speed and climb rate.
First production Me 163 B-0 variants, produced in early 1943, were armed with twin 20mm Mauser MG 151/20 cannon with 100 rounds per gun. By the 47th production variant, the Komet was upgunned to twin 30mm Mk 108 cannon. The designation was then changed to Me 163 B-1. The B-1 had 60 rounds per gun. This armament met with some criticism from contemporary engineers. The Mk 108 had a low rate of fire and poor reliability. Statistically, the weapon failed once per every 100 rounds fired. In the constantly changing conditions of aerial combat, the 163 could simply run out of shells before having a chance to successfully destroy a heavy bomber.